Natural gas usage in automotive vehicles is rapidly increasing throughout the world, both because of its operating and cost advantages over gasoline and diesel fuel and because the air pollution problems produced by the latter fuels have become so acute, particularly in urban areas, that national and local governments are requiring vehicle manufacturers and fuel suppliers to intensify their efforts to enable vehicles to operate on alternate fuels. There are over 30,000 automobiles, trucks and buses operating on natural gas in the United States and about twenty times that number operating worldwide. Such vehicles draw their gas from heavy-walled high pressure cylinders (usually steel) secured to the vehicles' frames.
In order to contain sufficient gas to enable a reasonable range of operation for the vehicle, such cylinders are typically charged to an initial pressure of 2,000 to 3,000 psi. Since local gas distribution lines typically operate in the range of 100 to 150 psi, fueling stations must be built with sufficient compression capacity to charge the gas at the required high pressures and to fill the vehicles' tanks through high-pressure lines. Usually, such fueling stations are built to supply fleets of a specific number of vehicles and are sized for a known average fuel consumption per day. Because the costs of building the stations are almost directly proportional to the rate at which the vehicles must be filled, station owners are faced with a choice between the prohibitively high costs of a large compressor to achieve the same rapid filling rates (usually a few minutes) which are attained with filling gasoline or diesel fuel tanks, or with putting in a much smaller, but still very expensive, compressor systems that achieve the necessary pressures and delivered volumes over a 12 to 18 hour period.
Practically all systems in use are of the latter type, and require that a majority of the vehicles be tethered to gas feed lines overnight, while the compressors slowly build up pressure in the tanks. The types of fleets so supplied are those limited to day-time or single shift use in local service. The vehicle-mounted tanks are usually sized to permit ranges of about 75 to 125 miles (121 to 202 km) without refill. The high capital costs and slow-fill limitations have severely hampered the growth of fleet usage of compressed natural gas for vehicles. A further handicap is the high electrical energy cost for operating the compressors.
Most users are unwilling to have their vehicles tied up overnight to fill the gas tanks, and the alternative of installing compressors large enough to fill the tanks in 5 to 10 minutes is so expensive that it is impractical and there are essentially no "quick fill" stations of this type.
U.S. Pat. No. 2,574,177 issued to R. Godet shows the use of automotive vehicle wheel or motor to drive a compressor to pressurize the gas in the fuel tank; however, this method has the same problem as the compressors previously mentioned in that it takes too long to build up a sufficient amount of pressure and most vehicles cannot be tied up for that length of time.